As much as I would love to delete Steam from Windows and move entirely to Linux that is not yet an option for me, at least not yet. Hopefully in the near future. That being said with limited space on my Linux partition installing 10-15 gigs of game data that is already on my computer is a bit annoying. Currently Steam does not recognize GCF files if they are on a NTFS partition(neither symlink nor adding the folder to the Steam libraries will work). A feature that recognizes these files would save users who dual boot a good chunk of space. I apologize if this is something not possible in Linux, my knowledge on the topic of file systems is very lacking and thank you for reading.

Currently Steam does not recognize GCF files if they are on a NTFS partition(neither symlink nor adding the folder to the Steam libraries will work).

A symlink worked for me in OpenSuse 12.2, linking the entire Steam data directory (~/.steam IIRC?, not in Linux atm to check) directly to my NTFS storage drive. I've only installed a few games so far, including TF2 which has had updates since, but it seems to have worked fine. Being able to have the main data files co-exist with Windows would be great though as I do still use both for gaming.

I just tried symlinking gcf files, and found that it worked. However, I had previously tried symlinking my entire steamapps directory, which failed for tf2. Symlinking the steamapps/common directory also seems to work, at least for Dungeons of Dredmor. The down side is that it's still necessary to download duplicates of custom files (maps, models, materials, etc).